This application is based on application No. 2000-250256 filed with the Japanese Patent Office on Aug. 21, 2000, the content of which is incorporated herein by reference.
(a) Field of the Invention
The present invention relates to a negative electrode for lithium rechargeable batteries and lithium rechargeable batteries, and particularly, to a negative electrode having an increased diffusion rate of lithium ion and in which a large amount of a non-aqueous electrolyte is immersed.
(b) Description of the Related Art
As electronic products tend to be more and more miniature in size, lighter in weight, and higher in quality and performance, there are demands for lithium rechargeable batteries exhibiting higher capacity.
Currently, a negative electrode for lithium rechargeable batteries is produced by coating a slurry including a carbon material as a negative active material and a polymer binder on a collector such as a copper foil, drying the coated collector and then roll-pressing the dried collector. In the resulting negative electrode, the carbon material is impregnated on the collector.
Several methods have been suggested to increase capacities of lithium rechargeable batteries, and the most effective method is increasing the amount of active material contained in a battery. To increase the amount of the negative active material without increasing the total volume of the battery, the thickness of the negative active material film on the current collector should be reduced. This may be accomplished by pressing procedures in which a negative electrode prepared by coating a negative active material slurry on a collector is pressed, resulting an increase in density of the negative active material.
However, there are some problems in the case where the negative mixed material is dense. Such a higher density decreases the porosities of the negative active material slurry so that it is difficult to immerse an electrolyte to the negative active material, and decreases the diffusion rate of lithium ion for the negative electrode so that the intercalation reaction of the lithium ion does not readily occur and the charge and discharge efficiency decreases.
The drop of diffusion rate of lithium ion is larger as the discharge rate is higher. Even though the amount of the carbon material increases in the pressing procedures, the discharge capacity decreases and the cycle life characteristics deteriorate during the discharge at a high rate.
It is an object of the present invention to provide a lithium rechargeable battery which has a higher charge and discharge efficiency and higher discharge capacity and a good cycle life during discharge at a high rate, resulting from increasing the retention of electrolyte in the negative electrode, and increasing the diffusion rate of lithium ion.
These and other objects may be achieved by a negative electrode for a lithium rechargeable battery including a carbon material in which lithium intercalation reversibly occurs and at least one metallic oxide selected from yttrium oxide, cerium oxide, and titanium oxide.